Chan IQ Meas Time and IQ Ref Time (TD-SCDMA)

Menu Path: Trace > Data > Channel 1 Chan > IQ Meas Time
Trace > Data > Channel 1 Chan > IQ Ref Time

When TD-SCDMA Demodulation is enabled, the IQ Meas Time and IQ Ref Time traces are the demodulated time data results, sampled at the symbol times, for the specified code channel (Code Length) and code layer (Spread Code Length). IQ Meas Time is the data results for the measured input signal. IQ Ref Time trace data is the data results that would be derived from an ideal input signal (reference signal).

Concepts

The VSA's demodulator produces two signals: I/Q Measured and I/Q Reference.

IQ measured signal

The IQ measured signal is the result of resampling the data to one point per chip and applying carrier locking, symbol locking, IQ origin offset and burst amplitude-droop compensation, filtering, system gain normalization and despreading to the incoming signal.

IQ reference signal

IQ reference signal is the ideal signal that the VSA generates from the IQ measured signal demodulated data bits. The VSA detects bits from the measured IQ signal and reconstructs a sequence of ideal I and Q states. These are then treated as ideal impulses and are baseband filtered according to the reference filter and added together to form the IQ reference signal. The resultant IQ reference signal is then used compare and analyze against the IQ measured signal.

Compensation

Demodulation is performed with carrier lock and chip lock. In addition, the VSA compensates for I/Q origin offset and burst amplitude-droop.

Time-Domain Displays

The VSA's demodulator produces time-domain data. If IQ Meas Time is selected, the VSA shows the I/Q measured signal in the time domain. Likewise, if IQ Ref Time is selected, the VSA shows the I/Q reference signal in the time domain.

The data can be displayed in a variety of trace data formats, including I-Q, Constellation, Q-Eye, I-Eye, and Trellis-Eye formats (see Trace Formats (Digital Demodulation)).

If normalization is OFF, the VSA shows the instantaneous magnitude. If normalization is ON, the VSA scales the IQ measured and IQ reference traces to map them onto the unit circle, which yields a unitless y-axis.

See Also

Chan Trace Data

Trace Data (TD-SCDMA)